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What's the difference between a "runaway prop" and a "feathered prop"?
My father was a P-51 fighter pilot in WWII. Another P-51 flown by a buddy of his suffered a "runaway prop", and as a result of that, the plane could not maintain its normal high speed, and in the end, the engine overheated and the plane exploded over the English Channel.  Luckily, the pilot, Major Foy of the 357th FG, had noted excessively high engine temperatures, and bailed out just before it exploded.  What would cause a "runaway prop" of the variable prop to create a loss of thrust and a high engine temperature?

A "run away prop" is caused by a failure of the pitch control mechanism of a constant speed propeller.  Feathering turns the prop blade as close to 90 degrees to the wind as possible, minimizing the effects of the airstream.  This obviously reduces drag and is used when an engine is shut down.
A run away condition is created when the propeller malfunction causes the blade to move to the "fine" setting, which is used at slower air speeds.  It is the opposite of being feathered in that now the prop blades are much more angled to the wind as in a windmill.  The force of the airstream literally now turns the engine to excessive rpm.  The prop is at the wrong pitch for its airspeed, much like a truck dropping into low gear at highway speed.  The engine rpm redlines and causes overheating, while the drag of the improperly set prop slows the plane down.
Thankfully, the pilot was aware of the danger and was able to get away.

If the effect of this is an overheating/exploding engine, how do you survive this in an aircraft where you can't easily bail out?

Related incident: Atlantic Southeast Airlines Flight 2311

To target the question, the difference between the two prop settings is something approaching 90 degrees.

@PhillipCopley by paying attention to your aircraft and bailing out in time. It wasn't easy to get out of any WWII era aircraft, but it was doable.

@FreeMan He asked "how do you survive this in an aircraft where you can't easily bail out". Modern constant-speed prop GA and commercial planes don't have ejection seats, and it's not standard practice to pack parachutes for all on board. This applies to more than WWII-era military aircraft.

Your point is valid, @RoyTinker, I was thinking in terms of the OP which specifically mentioned a P-51 and that got me into the WWII mindset. I wasn't thinking of a more modern multi-seat GA aircraft. In that light, it's better off as a whole new question.

@PhillipCopley: You don't.

@PhillipCopley, engines of civilian aircraft are not as prone to exploding as the massively overpowered and very temperamental engines used in fighters, which additionally often had fuel tank right behind the engine. Still, runaway propellers do cause fatal accidents occasionally as the drag from one propeller in full flat pitch is often high enough to get the aircraft out of control.

The prop regulates engine rpm using a flyweight governor (functionally similar to the ones on steam engines) which drive propeller pitch coarse or fine as required to keep rpm constant, regardless of throttle setting. The governor either controls an electric signal (curtiss electric) or engine oil pressure (hydramatic propellers) to provide the driving force to rotate the blades.
The aerodynamic loads on the blades are always trying to drive them to full fine pitch and the servo forces varied by the governor push against that.  If the governor fails or the oil supply to the prop hub fails such that the governor is not able to vary the blades against air loads, the blades will naturally relax to the full fine position, which unloads the engine and allows it to overspeed; how badly depends on the throttle setting.
So if a prop runs away, you'll be cruising along minding your own business and suddenly the RPM will surge past the redline until you yank the throttle back.  It's not that different from pushing in the clutch on a car while you've got the pedal down.  You'd better let off on the gas post haste if you don't want to destroy the engine.
Overheating is something else.  A runaway happens very quickly, whereas an overheating engine is more of a long term problem.  Not sure if the overheating was directly related to the prop problems.  If you'd had a runaway but were able to reduce the throttle enough to keep the engine at or below redline rpm, I'm not sure why you'd get overheating with the power cut way back. It's possible that to avoid descending, he kept enough throttle on to maintain altitude but in doing so the rpm remained well above redline and the extended overspeed operation overheated the engine (Mostly from the excess heat generated by the too fast piston movement).

the frictional heating created by an engine being forced to spin in overspeed is enough to wreck the engine and start it on fire even if the engine itself is shut down (mags off) while windmilling.


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Is there a maximum horizontal acceleration for passengers?
Are there any regulations regarding the maximum acceleration forces that passengers should experience during takeoff/flight/landing?
Or what would be considered to be an acceptable horizontal acceleration? 0.5g? 1g?
I am contemplating how to achieve very good STOL characteristics for a small  commuter aircraft while still maintaining a high wing loading.

I really like the question as a passenger plane is long and passengers from different parts of the airplane may experience different accelerations depending on the combination of linear and angular accelerations.

What sort of scheme were you planning to use that would come anywhere close to this: rocket assisted takeoff?  A steam or electromagnet catapult?  I suspect you'll be limited by economics more than passenger comfort.

@ChrisStratton I am not really sure yet. But considering that all these VTOL startups need to achieve a thrust-to-weight ratio >1, a thrust-to-weight ratio around 0.5 and therefore an acceleration around 0.5g might be feasible for a slightly larger aircraft (about a dozen passengers). I don't think rockets or catapults make sense from an economical or operational point of view.

Australian document AS 3533.1 prescribes a maximum 2g/3g for amusement ride, so you have some freedom. Note that very high accelerations are acceptable (30g if you wish) but not for any duration. When coughing, the body experiences a 3g acceleration. This is the key: how long will it last?

It depends on several factors:
1) How long is the body subjected to these forces?
2) What's the posture of the body?
3) To what extent are the passengers used to g forces (for example due to training)?
...
However, early experiments showed that untrained humans could withstand g forces as much as 20 g for less than 10 seconds, to 10 g for 1 minute, and 6 g for 10 minutes.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

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What is an accurate expression to calculate IAS as a function of TAS?
Does anyone know a good source for an expression of IAS as a funtion of TAS? I was hoping to find an accurate IAS equation that is only dependent upon TAS, static pressure and static temperature.

You might look at Ed William's aviation formulary.
http://www.edwilliams.org/avform.htm#Mach
From there:
> The airspeed indicator measures the differential pressure, DP, between
> the pitot tube and the static port, the resulting indicated airspeed
> (IAS), when corrected for calibration and installation error is called
> "calibrated airspeed" (CAS).
>
> For low-speed (M<0.3) airplanes the true airspeed can be obtained from
> CAS and the density altitude, DA.
>
>   TAS = CAS*(rho_0/rho)^0.5=CAS/(1-6.8755856*10^-6 * DA)^2.127940
> (DA<36,089.24ft)  Roughly, TAS increases by 1.5% per 1000ft.

Note that you can go from TAS to CAS, but you will need help getting to IAS, specifically the instrument error for that AS indicator in that aircraft.

TAS : True Air Speeda
IAS : Indicated Air Speed
CAS:  Calibrated Air Speed (reference airspeed based on  an idealized Pitot tube)
IAS = CAS + Ki, where Ki is an error component specific of your instrument
The conversion between TAS and CAS (and IAS) needs also to take into account the variation of air density (i.e. altitude).
So the conversion requires a bit more parameters.
A good answer is provided here:
How do you convert true airspeed to indicated airspeed?

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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What runway is used in a 90 degree crosswind?
If an airport has runway 09/27 and the wind is at 180 or 360, which runway is used? Is it possible for both ends to be used depending on the amount of traffic?

Disagree with the duplicate suggestion; this question is clearly about the specific case of direct sidewind, not about runway selection in general.

@aCVn well if there isn't a prevailing wind then all of the other factors listed there will be the important factors.

One would basically follow the same guidance as if the winds were calm:  If the field is tower controlled the controllers will pick a runway.  There may be a primary runway direction preferred in these circumstances for noise abatement, traffic routing, (i.e. Instrument Approach or Standard Instrument Departure procedures favoring one runway over another) or other considerations, otherwise they might consider whether the winds are forecast to shift to favor one or the other and base their decision on that.
At a non-tower controlled airport pilots would be expected to monitor a common traffic frequency and follow what others are doing.  And if you are the first or only person there, lucky you... take your pick!

Even at a towered airport, you may get to take your pick if the winds are calm (or light and variable).  One of the weirder ATC calls I've gotten: "Hold short of runway 33 for departing aircraft on runway 15, caution wake turbulence."  Opposing arrivals would be more difficult to manage due to the potential for go-arounds, but I've seen an example of that too.

Another consideration would be which direction has an instrument approach. Even on a VFR day arriving traffic might have to descend through clouds, the tower might favor the runway with an approach.

@JSCarry, good point.  That's kinda what I meant by "traffic routing" but I expanded my explanation for clarity.  Thanks!


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Aerodynamics and fuel consumption of a powered glider
I want to optimize the flight distance of a powered glider model airplane, without the use of soaring. I've studied some aerodynamics books, but still feel unsure about my conclusions. Please tell me if I'm wrong in the following:
1) The best fuel economy (liters per km) is for planes with the highest lift/drag ratio, typically so called gliders. The reason a 747 doesn't look like a glider to save fuel, is that it would be too difficult to build strong enough wings of that dimension.
2) Gliders are typically designed so that the best lift/drag ratio is when the airplane is in cruising mode with zero attack angle (horizontal). This is typically also when all control surfaces are neutral.
3) Optimum long distance cruising speed is at max lift/drag ratio, and when the lift is equal to the aircraft weight, given that the engine and propeller are also optimized for it. In other words, the speed where it sits stable in the air without any control. I can find this speed for my model glider by flying it at zero attack angle and with neutral control surfaces, and then increase the throttle gradually until the plane stops sinking.
4) Although the lift/drag ratio varies with speed, it varies very little around the speed that is optimum for long distance cruising. This is because lift-induced drag is a very small component of form drag (overall drag) at that speed. In other words, form drag is very close to proportional to the square of the speed.
5) If I want to increase the weight of the aircraft (for example add more batteries), all I have to do is fly proportionally faster to stay in the same zone of optimization for distance. Lets say the normal take-off weight of the glider is 1.4 kg. I quadruple the take-off weight to 5.6 kg. The lift equation says that my speed must now be doubled to make the airfoil provide four times the lift. This new speed will be very close to optimum cruise speed for distance, because of 4) above.
7) The speed has doubled, which means the drag has approximately quadrupled, so a new engine and propeller with four times the power and optimized for twice the speed must be installed.

Point #1 is wrong.  The reason the 747 (and other airliners) doesn't have wings like a glider is that it travels at high speed.  You could probably get much more fuel efficiency with glider wings (which wouldn't be that hard to build) and a 50 kt airspeed, but I suspect few people would be willing to fly with your airline :-)

Point #4 is also wrong. At best L/D induced drag is half of overall drag. What varies little around best L/D speed is overall drag - lift equals weight and does not vary, so near the flat optimum, drag will vary little as well.

What is point #6?

Thanks jamesqf, that makes a lot of sense!

Thanks Peter Kämpf. There is no #6, I made an error. But I don't understand your point. Looking at a drag/speed diagram, I can see that lift induced drag is very strong at low speeds and almost doesn't exist at high speeds, where parasitic drag is the major (only) component. Around best L/D, the drag equation must still be valid, so overall drag must vary a lot with speed (however the lift induced portion of it is probably weak). Or am I missing something here?

Which diagram do you talk about? Also, an optimum is defined by a zero gradient, so any changes near it must be small.

I can talk about a couple of these...

3) Optimum long distance cruising speed is at max lift/drag ratio, and when the lift is equal to the aircraft weight, given that the engine and propeller are also optimized for it. In other words, the speed where it sits stable in the air without any control.

Well, there are two speeds you're talking about:

The most efficient cruising speed, which is also the speed that maximizes L/D, which is also the best glide speed.
The "trim speed", which is the speed where the aircraft tends to maintain a constant pitch ("sit stable in the air") when the pilot is not applying any forces to the control.

For full-scale aircraft, the trim speed can generally be altered by the pilot in flight, using the trim wheel (or whatever trim control that aircraft has). So, the trim speed is usually not equal to the best glide speed.
That said, you certainly can (and it's probably a good idea to) design your powered glider so that its trim speed is constant, and equal to the best glide speed.

I can find this speed for my model glider by flying it at zero attack angle and with neutral control surfaces, and then increase the throttle gradually until the plane stops sinking.

Yes, you can find the trim speed (but not the best glide speed) of your model glider by controlling the throttle so that the height remains constant. If the controls are neutral and your aircraft is not pitching, then it is flying at trim speed.
(I'm not sure what you mean by "flying it at zero attack angle", since you can't explicitly control the angle of attack without moving the control surfaces. For steady flight, the angle of attack is determined by the speed and the bank angle.)

7) The speed has doubled, which means the drag has approximately quadrupled, so a new engine and propeller with four times the power and optimized for twice the speed must be installed.

That's almost right. If the speed doubles, then the drag quadruples. But power equals force times speed, so if the speed doubles, and the drag quadruples, then the needed power increases eightfold, not fourfold.

Responses to your comments:

However, as I understand it the "trim" is just a minor adjustment to the elevator, correct? So in effect we are nudging at the angle of attack so the lift perfectly matches the weight and the plane can sit stable, but we aren't really flying at the optimum L/D?

I wouldn't call it "just a minor adjustment". In a Cessna 172, trim is what determines whether the aircraft flies at 55 knots or 155 knots. Other airplanes and gliders work the same way: there is one particular speed at which the aircraft will fly steadily without any force on the control stick, and trim is used to determine what that speed is.
Trim isn't used for making the lift match the weight. If the lift is too high, then the aircraft will begin climbing (or stop descending), and if the lift is too low, then the aircraft will begin descending (or stop climbing). You control this by using the stick and the throttle.
The aircraft can "sit stable" with the trim in any position, but for each trim position, there is only one corresponding speed at which the aircraft will fly steadily without force on the stick.
(There's an exception to the above: with some aircraft in some circumstances, if the trim is too far back, then constant forward pressure on the stick or yoke is required in order to prevent the aircraft from stalling.)
If you're sitting in an aircraft and you want to fly at optimum L/D, you'll usually do that by knowing what airspeed corresponds to optimum L/D, and setting the trim for this airspeed. (The process for setting the trim appropriately is: use the stick to fly at that airspeed, hold the stick in place, and then use the trim control to relieve the force the stick is exerting on your hand.)

I'm just assuming that airfoils are designed to be at their best L/D at zero angle of attack, is that really the case?

I doubt it. In particular, some aircraft have symmetric airfoils, which have an L/D of zero at zero angle of attack.

When I said "flying at zero attack angle", I mean that the plane sits completely horizontal in the air, and it does so without any compensation from control surfaces.

If the plane is completely horizontal, that's zero pitch, not zero angle of attack. Zero angle of attack is when the nose is pointed exactly into the oncoming air, rather than higher or lower.
The pitch that an airplane settles at depends on both the trim and the power setting.

Last part doesn't seem right to me. If you look at it from the perspective of the engine, it creates a forward force. This force is constant, no matter the aircraft speed (taking aside the fact that a propeller cant be equally effective at all speeds). However the drag is related to the speed, and the drag is four times stronger. So it feels to me like the needed power is only four times more, not eight.

Well, the thing there is, an engine doesn't really create a constant force. In particular, you need to produce enough force to counteract drag. If your aircraft experiences four times as much drag, then your engine also needs to produce four times as much thrust in order to fly the same way.
So in order to fly twice as fast, you need to make the engine produce four times as much force (either by opening the throttle more, or by using a more powerful engine). The engine also needs to operate at twice the airspeed. Power is force times speed, so together, these two facts mean that the engine needs to produce eight times as much power.

Further responses to your comments:

Re angle of attack and pitch, I might have just confused the terms. As I understand the terms, "angle of attack" refers to the angle of incoming air relative to the chord of the airfoil, so it relates to the wings only. Pitch is the angle of incoming air relative to the aircraft itself. So if the wing chord is mounted exactly horizontal, angle of attack and pitch are identical.

Pitch doesn't have anything to do with the angle of the oncoming air; it's exclusively defined by the way that the aircraft is oriented in space, relative to the horizon. Specifically, pitch is the angle by which the nose is pointing above or below the horizon. If it's pointing 10 degrees above the horizon, the pitch is 10 degrees; if it's pointing 20 degrees below the horizon, the pitch is -20 degrees. This is regardless of how the aircraft and the air are moving.

It makes more sense to me when I imagine putting a piston engine with a propeller in a wind tunnel. Would the thrust force of that engine/propeller vary greatly with incoming airspeed when running the engine at constant power? I can't imagine why it would. As the air speed increases, the engine would increase its RPM to exert the same power on the air, and the propeller efficiency would vary slightly, but the engine power would still be the same. And overall the thrust force would be approx the same. Or am I thinking the wrong way here?

Well, the best way I know how to put it is "that's physics". If you want to push something in the same direction that it's already going (as an airplane propeller does—it pushes the air aft, even though the air is already moving aft), and you want to push it with a constant force, then the faster that thing is going, the more power is required in order to push it. I don't think it's easy to see why this is the case, but this is, in fact, the case.
Maybe it would be helpful to imagine an airplane flying straight up. Imagine that this airplane is heavy but sleek, so that the drag is very small compared to the weight. Then, in order for this airplane to fly straight up at any speed, its engine will simply have to generate thrust equal to the airplane's weight. (The only time the engine would need to generate more thrust than the airplane's weight, is when it's making the airplane accelerate.) And yet, if this airplane were to fly twice as fast, surely the engine would need to generate more power, right?
The moral of the story is that power depends on both force and speed. That's physics; there's no way around it. If you had an engine that generated a constant amount of thrust, using a constant amount of power, regardless of speed, then you'd be able to make a perpetual motion machine out of it.

minor nitpick: Zero angle of attack is when the direction of movement is parallel to the chord line, the line connecting the nose and the trailing edge of the airfoil. The other angle is the zero-lift angle of attack.

@PeterKämpf Thanks, I removed my mistaken statement there.

Thanks Tanner, this was enlightening, I stand corrected. However, as I understand it the "trim" is just a minor adjustment to the elevator, correct? So in effect we are nudging at the angle of attack so the lift perfectly matches the weight and the plane can sit stable, but we aren't really flying at the optimum L/D? I'm just assuming that airfoils are designed to be at their best L/D at zero angle of attack, is that really the case? I hope I'm making sense here.

Tanner, when I said "flying at zero attack angle", I mean that the plane sits completely horizontal in the air, and it does so without any compensation from control surfaces. Perhaps that is impossible because center of lift isn't exactly over center of gravity. Looks like Im simplifying here. Just trying to understand how to get to the point of most economical flight.

Tanner, the last part doesn't seem right to me. If you look at it from the perspective of the engine, it creates a forward force. This force is constant, no matter the aircraft speed (taking aside the fact that a propeller cant be equally effective at all speeds). However the drag is related to the speed, and the drag is four times stronger. So it feels to me like the needed power is only four times more, not eight.

@BjörnMorén I've edited my answer to include responses to your comments.

Thanks, the trim of an airplane makes more sense to me now. Re angle of attack and pitch, I might have just confused the terms. As I understand the terms, "angle of attack" refers to the angle of incoming air relative to the chord of the airfoil, so it relates to the wings only. Pitch is the angle of incoming air relative to the aircraft itself. So if the wing chord is mounted exactly horizontal, angle of attack and pitch are identical.

Tanner, my example involves an ideal engine/propeller combo (that's why I wrote that propeller efficiency can be ignored). For an ideal engine, the speed at which the aircraft is traveling (i.e. incoming air speed) has no effect on engine thrust. A turbojet is almost an ideal engine in this regard. A piston engine with a propeller is closer to an ideal engine, than it is to "doubling the power for each doubling of speed". You can read more here: https://www.quora.com/Why-are-jet-engines-specified-in-pounds-of-thrust-while-propeller-engine-ratings-are-given-in-horsepower

Tanner, it makes more sense to me when I imagine putting a piston engine with a propeller in a wind tunnel. Would the thrust force of that engine/propeller vary greatly with incoming airspeed when running the engine at constant power? I can't imagine why it would. As the air speed increases, the engine would increase its RPM to exert the same power on the air, and the propeller efficiency would vary slightly, but the engine power would still be the same. And overall the thrust force would be approx the same. Or am I thinking the wrong way here?

@BjörnMorén I've edited my answer again with more responses.

Thanks Tanner, now I understand pitch and angle of attack better.

Tanner, regarding "that's physics": In that case, how is it possible that a turbojet has a thrust that doesn't vary with aircraft speed? According to your theory, that would be physically impossible, right? I try to imagine this physics problem as if the incoming air consists of lots of tiny balls at a certain speed. What the propeller does is hitting them like a bat to give them a higher speed, with a resulting opposite force. The speed difference between incoming balls and outgoing balls is all that matters when it comes to thrust, i.e. incoming speed is not relevant.

Tanner: If incoming airspeed would be relevant, you would break the energy conservation law. Besides overcoming the drag, where would the extra energy from the engine/propeller go? Take away drag (as in your vertical example) and you have a space ship. Thrust on a space ship doesn't vary with speed.

@BjörnMorén I'd like to make a new question post about the power question, so that you can get a good answer to it. Does that sound all right? Alternatively, you can post a question yourself if you'd prefer.

Tanner, that sounds good, please make a new question, and I'll take part in that discussion. BTW, happy new year!

@BjörnMorén I've posted the question here: https://aviation.stackexchange.com/questions/58606/in-order-for-an-airplane-to-fly-twice-as-fast-how-much-more-power-does-the-engi If you have anything to add to the question, please feel free to post it as a comment on that question. Happy new year!

@BjörnMorén Come to think of it, I really think it's best if you post the question. I've copied and pasted the question text into this chat room, so you can copy and paste it again into a question of your own if you like: https://chat.stackexchange.com/rooms/87739/power-and-speed

I've posted a new topic, but I trimmed the question down to simplify. Feel free to add your line of reasoning as an answer: https://aviation.stackexchange.com/questions/58622/change-in-power-requirement-when-weight-and-speed-changes


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Process for Compensator in Altitude Hold
Trying to understand autopilots on a technical level. When making an altitude controller there is a compensator Gc that is used to acquire a Pitchcommand which is passed to an attitude controller (the attitude controller uses a PID loop which I understand). What is the process of creating that compensator? I've read that a PI compensator is less reliable and more complex than a lag compensator. But as a rough approximation (still trying to figure it out) of what needs to be done for a lag compensator you need to have a linearization of the aircraft model, apply root locus, adjust poles, and acquire a transfer function. If anybody could specify what would need to be done (correcting my missing/incorrect understanding) that would be very appreciated.

A lag controller is basically an amplifier whose input is proportional of the present error, that is the difference between the current altitude and the target altitude

With low amplification the trouble is the lack of response as long the error is small.
With great amplification we have an overshoot effect with continuous oscillation around the target altitude.
The best simple low cost compensator consists of an PID
Please refer to this website:
https://en.m.wikipedia.org/wiki/PID_controller
The PID has 3 adjustable inputs:

A proportional input « P » somehow similar to a lag amplifier
An integral input « I » that is proportional to the error but also to the duration of the error, therefore an error as small it may be will be corrected with time and will decay
A derivative input »D » which is proportional to the slope of the error that is the error evolution, therefore it has a predictive value. Therefore the D input will neutralize the tendency of an error to appear or to increase.

The adjustment is done by small steps,
-you start by setting to minima the I and D inputs, and set the P input to get the best non overshooting response.
-In order to reduce the remaining error with the previous adjustment you increase the I input by steps and verifying you don’t get overshoots
-In order to avoid drifting error you act on the D input, increase the input so that you obtain a little overshoot that you correct by reducing the I input.
Trial and error adjustments could be useful


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Would an F-15 or similar stand in be able to continue flight at high speed if it lost its canopy?
Let's say for whatever reason, miscued ejection system perhaps, a jet in flight at exactly mach 1 blew its canopy but did not eject the pilot.  And we can assume the altitude is fairly low (to exclude the attendant freezing/suffocation that would ensue).
My friend and I have been arguing about this.  He insists that it would result in catastrophic damage to the jet due to a sudden lack of aerodynamic stability and that the pilot would be grievously harmed or killed.
For my own part, I'm just not so sure.  It seems to me that if said pilot was wearing a JHMC or some helmet with visor that he'd have plenty of time to react and set the aircraft safely down.  And could probably do 400 knots comfortably on his way home to complain about the faulty ejection.
And I figured a jet is so very large and aerodynamic over its entire body, without the canopy it'd be less so, but still not so badly that the thing would be torn to pieces as a result, right?
The only similar story I could find was of an F-14 that lost its canopy, but the pilot only mentioned going 320 knots and it not being as loud as he expected.
So mach 1 is a key part of this question, I think.  I can't find a reasonable answer to settle our dispute, someone please help!  I really want to settle this.  Thanks in advance.

Felix Baumgartner went supersonic, basically wearing a space suit.  However, I don't think a typical F-15 pilot is so well protected.  He may well be choked by his helmet-chin strap as the intense winds pull the helmet up.  His facemask would probably break away and pound him in the head and body with incredible force.

@abelenky: Not to mention that Felix went supersonic at altitudes where the atmosphere is way way way less dense (and the aerodynamic forces on the human body are correspondingly much much much weaker) than at those under discussion here.

Several F15's have had incidents of canopy loss, and all the ones I have found came back and landed safely. The latest incident I can find was in 2014 off Okinawa. I see no reason why there would be any such catastrophic failure of anything on the aircraft unless the canopy impacted some part of the aircraft as it departed. Ejection systems are designed to allow the crew to exit the aircraft at pretty much the entire flight envelope. Yes, at supersonic speeds the crewmember will probably be sore for quite some time, but it's been tested and used in real life and it works.


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Acoustic analysis from an aircraft engine?
I have found it surprisingly easy to find information on jet engines; however, I've been unable to find acoustic information so I can make a noise spectrum model.  I'm looking for oscillations from 100Hz up to 1MHz. I could make some guesses based on the number of blades, diameter and rotation speed, but I believe this information is out there because there exists noise reduction insulation on aircraft, and environmental noise rules.  In my search, I've found that NASA as analysis tools for acoustic liners, but nowhere have I found a study where these frequencies are described (I realize they will be different for different engines)
Ideally, what I'm trying to find is a decibel vs. frequency chart.
My motivation is purely academic as I have found (I think) that certain capacitors inject noise via ultrasonic oscillation into electronics, and I'm trying to find the frequencies involved. (I'm pretty sure that I'm going to have to make a blade/stage/rpm/thrust model for the noise, but I'm really hoping that the acoustic information is out there.)  At this point, it's possibly down to nomenclature and that I am not looking for the correct term as aviation is full of lingo.
Has anyone ever seen acoustic data for a jet engine anywhere?

Have you looked at fly-over spectrograms? These are available in scientific literature, but of course they include the complete aircraft. Is that maybe what you're looking for? Otherwise there are some very simple models to model the noise of the engine based on some parameters.

@Daniel No, but I'll take a look for those.  The complete aircraft would be fine, and I'm just hoping to get a general feel for concentrations of noise energy.  I'll dig in the library.

Is that even a thing, 1MHz acoustic noise?

Do you mean something like the graph in this answer, except up to 1 MHz?

No one can hear anything above 20khz and most people can't hear anything above 15khz. 20khz-1Mhz is not noise and I don't know any reason anyone would collect such information.

Found one in an earlier answer, the original article seems to be removed.

@Koyovis Both of those are very close to what I'm trying to find.  I have noticed that my electronics, that are designed to read very low currents and the system is a very good "aircraft" detector.   I think Bianfable's link would be the most nearly correct.  Thanks to both of you.

@Bianfable  see above

"certain capacitors inject noise via ultrasonic oscillation into electronics, and I'm trying to find the frequencies involved."  So, you are trying to see if you can detect electronics noise in the spectrum of a jet engine?  Forget it.  Although I'm sure the FADEC and electronics do have some hum to them, it will be drowned out by other noise by multiple orders of magnitude.  I think you'd have to put the microphone inside the FADEC to hear such noise.

@Pilothead "noise" is not an acoustic phenomenon only, any unwanted and/or random signal in acoustic or EM spectrum is noise by definition.

@Jpe61 I have profiles from several aircraft engines in the RF spectrum.  I'm interested in the acoustic only.  I can tell what type of fuel is being burned by the RF peaks.

Yea I was referring to Pilotheads's comment "20khz-1Mhz is not noise...". That frequency range is certainly not considered audible , but it can contain noise.

It strikes me that acoustical analysis of an engine like this would be something the manufacturer would do in an effort to improve noise insulation/reduction (like the saw-tooth nacelles seen on some engines), but wouldn't necessarily be made public. The public part would be mostly marketing "New! Improved! 32% quieter than our previous model!!" jargon.

@Jpe61 The question specifically names acoustic noise.

I know. You wrote: "20khz-1Mhz is not noise..", I think the most proper way to put that would have been "noise in the range of 20kHz to 1MHz is not acoustic".

Found some info in a really old TU Delft uni book on aircraft sound (VTH-78 from 1973, in Dutch, paper copy only). The pics are from a French article by Y. Covillard: "Unitės de measure dans l'acoustique aéronautique", published in l'Aeronautique et l'Astronautique, no. 32, 1971. The English notes are my translations.
Max frequencies are about 16 kHz, which makes sense since most articles are interested in audible noise. Unfortunately we don't have information on which bypass turbine engine was measured.

I don't really have an example or a proper answer, but you may be able to download a decibel/noise meter on your phone (such as Spectrum on iPhone), and use it at an airport when a jet flies by.  They tend to record sound levels and a frequency spectrum as well. I have used these before to get a general sense of the noise levels. As a previous commenter posted, these may focus only up to 16 kHz though. Perhaps there are also tools you can buy for cheap or rent that could measure in some of your desired range.

I'm not sure if this is what you are looking for, but here goes:
For example, Benshuai Lyu & Ann P. Dowling have studied the effects of lobed nozzles on installed jet noise. The article displays graphs plotting frequency vs. decibel of variable arrangements of jet nozzles. The graphs go up to 20kHz, which would be the upper limit of audible spectrum (*.
S. Khardi has published a study "An experimental analysis of frequency emission and noise diagnosis of commercial aircraft on approach" (link to pdf). The document contains several graphs displaying noise profiles.
*Your question does mention the upper limit of frequency range you are interested in as 1MHz, but in a later comment you mention "I'm interested in the acoustic only."
Quite frankly, if I understood your question correctly, the data/graphs you request are very easy to find with simple "jet engine acoustic spectrum" google search, so I suspect I've misunderstood something.


text:
What's the difference between a "flight line" and a "tarmac"?
I was at a conference where there was a discussion on ontology for assets.  There were two classification trees, one for assets on the flight line and one for assets on the tarmac.
What is the nuance between these?  Is it active aircraft vs. inactive aircraft?

The nuance is between aircraft that have been / will be flying imminently, and aircraft that are more than a few hours away from doing so.

Apron (U.S., ramp) is where aircraft refuel, load/unload, etc.
Flight line is, in the popular press, where aircraft are parked, maintained, and displayed.  This usage is duplicated by aeromodelling clubs, although their time scale is closer to minutes than hours. (Wikipedia claims, without substantiation, that flight line is the U.S. military term for tarmac, ahem, apron.)
Tarmac (U.S., asphalt) is a paving material, one possible surface for runways and roads.  It's not an aviation term.  Informally, it means apron: we hear about tarmac delays, never about flight line delays.

Tarmac (British English term, mostly, in the US it would be asphalt or blacktop) is more properly a paving material.  In addition to roads, it's also used for runways, parking areas, &c.

Good points.  Incorporated.


text:
What is the aircraft in the 'Be Altitude' album cover?
In 1972, the Staple Singers released the "Be Altitude" album, which has them posing in a jet engine's intake.

My question is what aircraft does that engine belong to? And why would someone let them use it for a photo shoot?

Its a Boeing 747 courtesy of Delta Airlines as per the album credits. Photo by Gerry Griffith. For the right amount of money its not that hard to take pictures in, on, or near jets.


text:
Does rolling or yawing affect the angle of attack?
If I'm on final in windy conditions and I need excessive rolling and yawing movements to stay on centerline and say, my pitch stays constant - does rolling or yawing change my AOA such that I could stall?

No that's not how it works.  You shouldn't need "yawing" movements on final before the landing flare.  That implies that you are using rudder to push the nose left or right to keep the runway sight picture where you want it, a very bad practice.
Never use rudder to stay aligned with the runway, except in the landing flare.  Other than that, only use rudder to keep the ball centered, or to side slip to lose altitude.  At all times, unless you are side slipping on purpose, use coordinated banked turns to stay aligned with the runway prior to the flare.
The rolling movements should be just those movements required to make coordinated banked turns to adjust heading to stay on centerline, or to get back on centerline.  Maybe 20 degrees of bank. Ball centered as much as you can keep it centered in bumps.
Moderate banked turns in a descent with ball centered create zero risk of stalling if speed is attended to.  Stall/spin accidents happen when pilots try to shove the nose with rudder to point it at the runway, causing uncoordinated flight, on top of sloppy speed control, so that if they get too slow, with the airplane slipping or skidding, when it stalls it flicks over the inside wing and down you go on your ride to oblivion.
If you are keeping bank angles within reason, ball centered, and speed on the proper approach speed, you won't stall the plane and normal control inputs will not get you close to stalling the plane. And with any modern plane, if you do stall it but the ball is centered, you won't depart in a spin and you can recover instantly.  Coordinated ball centered flight is the most critical item after speed control.

Isn't staying banked right down to just above the ground basically asking to have the engine under the low wing hit the ground?

Not for most aircraft.  In a cross wind you land banked with cross controls (ie, wind from left, left wing down and right rudder to stay aligned with the runway, basically landing in a side slip).  On large heavies with underslung engines there is not a lot of bank angle available before one engine contacts, and in those cases you fly to the runway in a level crab and align the nose with a big shot of rudder right before touchdown.  In most smaller airplanes including smaller jets you land with wing down side slip same as light aircraft.

@Sean That is a concern, and on aircraft like the 747 the recommendation is to touch down in a crab. See https://aviation.stackexchange.com/questions/58861/what-is-the-maximum-angle-between-an-airplane-and-runway-centerline-when-touchin/58864#comment154307_58864 for a discussion, and especially the comments.

@JohnK previously, I would have agreed with you about coordinated flight while on final, but as a result of flying Condor with coordinated flight mode turned on (due to not having rudder input on my joystick), I have begun to reconsider the importance of rudder for aligning the plane with the runway. When you consider how slowly a plane banks vs how quickly it can adjust yaw-- especially for the gliders that you and I fly--, I think you will agree that it is nigh impossible for us to do any degree of fine control while maintaining coordinated flight. I think we skid a lot more than we realize.

Rolling will increase the AoA of the wing that sinks and reduce the AoA of the wing that rises.


text:
Can roll be controlled through elevators in a fixed-wing aircraft?
In fixed-wing aircraft, roll is typically controlled through ailerons.
But I am wondering if roll could also be controlled through split, independently controllable left/right elevators?

Yes.
Fighter jets with split elevators can command a roll in the way you describe, see this answer for more info.
For an aircraft like a delta wing (tail-less) that lacks a traditional empennage these control surfaces are combined into an elevon to produce a mix use elevator aileron.
The Concorde is a classic implementation of this design. Flying wings like the B-2 also use this design.


text:
What components on a fully functional A-380 could fail in mid flight while still allowing the plane to land without loss of life?
I'm doing some research for a potential fan story in the Dresdenverse. Summary: a passenger is flying for the first time in an A-380. The A-380 is fully functional: it's the first flight after a complete maintenance and the pilots are very experienced. However, components slowly stop working on the plane, starting with small stuff: a seat won't recline, a folding tray won't fold open,... However, as time passes more and more components stop working and in the end, pretty much everything on the plane is malfunctioning. They only just make it to the airport, where they make a hard landing. There are minor injuries, but everyone makes it out alive. In the end, the passenger turns out to be a powerful wizard with a technology disruption aura who was being deported to his home country.
The question I have is: in this scenario, what is the absolute bottom requirements for this plane to be able to make it to the ground with no loss of life? I'm talking about ABSOLUTE here: it's okay if the plane after this is a mangled wreck which will never be able to fly again or even be examined for what went wrong. I just want the passengers to survive.

The Minimum Equipment List may be a good start for you - it lists every piece of equipment that is LEGALLY allowed to fail and still allow the aircraft to depart. The list for the A380 is extensive and details how many of each item can fail - the failure of such things would definitely allow the aircraft to fly as you ramp up to the more severe stuff. The obvious culmination would be several engine failures and reverting to Direct Law

You are basically asking about the whole design of reliability engineering of A380.

Oh, that's a fun one...
Let's start by imagining that all electronics and all moving parts on the airplane fail. It's still structurally intact, but there's no way to control the plane.
If this happens, the #1 problem is the spiral dive. The bank angle will steadily increase further and further. As the bank angle increases, the wings are less and less effective at holding the airplane up, so eventually... they stop holding it up.
In order to prevent the bank angle from increasing, the pilots must have some means of lateral control. This means that they must be able to control at least one engine, or at least one aileron, or the rudder.
This other answer states that if an Airbus's electrical system fails, "the system reverts to mechanical backup, where pitch control is achieved through the horizontal stabilizer and lateral control is accomplished using the rudder pedals."
So if you want as many things as possible to go wrong, while still being a survivable failure, I suggest:

All four engines fail.
The landing gear fails; it cannot be extended. (If the landing gear could be extended and retracted, the pilots could use it as a flight control.)
The entire electrical system fails, meaning that conventional control is no longer possible.
The trimmable horizontal stabilizer also fails, meaning that the only flight control available is the rudder.

If the pilots are sufficiently skilled, they will be able to maintain directional control, and avoid both Dutch roll oscillations and phugoid oscillations when they do. If the pilots are able to do that, then their job description becomes very simple: control the direction of the airplane in such a way that when it touches the ground, it's on a runway.
There's one problem remaining with using the rudder only, and that's that there's no way to control the airplane's descent rate. It'll simply descend at whatever rate it "wants to", aerodynamically. This descent rate may be similar to the descent rate of the so-called Gimli Glider (Air Canada Flight 143, which was a Boeing 767). I don't know what that descent rate was, but a couple of web pages describe it as being about 2,000 feet per minute, which is about 20 miles per hour. Keep in mind, that's 20 miles per hour straight down.
(If the pilots are really skilled, they'll induce a phugoid oscillation which is timed in such a way that the touchdown is gentler. But that sounds pretty unlikely.)
If you want to give your pilots even more of a thrill ride, you can have the rudder fail upon touchdown, or even a few seconds (10 or 20 seconds?) before touchdown. The effect will be pretty much the same as a car: the plane will continue in the same direction for a few seconds, but it'll inevitably start to veer to one side. It will likely run off the runway and into the grass.
All in all, the outcome will probably be exactly what you're looking for: lots and lots of components fail, the plane ends up a "mangled wreck", but everyone survives.
Side notes:

Even if the landing gear were working perfectly fine, the pilots might decide not to use it. If they extended the gear in flight, but the gear failed to retract, then it would cause drag, resulting in an increased descent rate, which could be disastrous. If they extended the gear just before touchdown, but the brakes failed, then they might overrun the end of the runway; if they ran into an obstacle, that could be even worse than making a gear-up landing.
As a little bonus, you could have the cockpit voice recorder and the flight data recorder both fail at the very beginning of the flight. This is likely to leave investigators more confused about what could have caused the accident.
I'm a Dresden fan too; let me know if you finish your story!

How does one control a phugoid with just the rudder?

@Sanchises With difficulty! :D I don't know the details, but I can make an educated guess. To damp a phugoid oscillation, you only need to do any one of four things: decrease the airspeed while it's high; increase the airspeed while it's low; lower the nose while it's high; or raise the nose while it's low. The rudder can be used to produce sideslips, which decrease the airspeed, so if I wanted to damp a phugoid with the rudder, my first attempt would be to give rudder input while the airspeed is high.

Rudder input (and accompanying coupled roll) tend to lower the nose.  Let a little speed build, then neutralize rudder, and you're above trim speed; you'll almost certainly get a little phugoid motion.

Back in the 1960s and 1970s, rudder-only radio control could be used to fly loops -- put the aircraft into a tight spiral, let speed build enough, and neutralize; the overspeed would raise the nose past vertical, across inverted, and then you'll apply rudder as you passed the bottom to prevent a whipstall.

Interesting... Have you included the landing gear in "all moving parts"? And does this need the rudder all the way until the plane has stopped on the ground? if not, what's the absolute earliest I can have it fail during the landing sequence?

@Nzall Good questions. I edited my answer to include that information.

As far as I can tell, the mechanical law was deleted on A380, likely because A320–A340 never ever reverted to it anyway. Complete hydraulic failure is more likely than complete electric failure and complete hydraulic failure renders the mechanical law inoperative anyway.

Probably not the answer you are looking for, but I would definitely recommend to read the book "QF32" by Richard de Crespigny about Qantas Flight 32. It is the captain's personal account of what can go wrong in an A380 suffering a major damage (uncontained engine failure, leading to multiple system failures), and how a competent flight crew can save the day with every single person on board walking away from the aircraft afterwards.
Quite an impressive read. It also gives an impression on the levels of redundancy in a modern aircraft like the A380.
The official final investigation report by the Australian Transport Safety Bureau may offer further technical insights to this event.


text:
What percentage or airplanes have engines
I heard that some airplanes don't have engines. how many airplanes in the world have engines?

A plane without an engine is typically called a glider.

Do you mean those that do not have engines by design, i.e., gliders, or airframes that have had their engines removed? As it stands it is unclear what you are asking.

I would say all of the registered airplanes except the gliders have engines.  I don't know that there is a world-wide registry containing all of them, you'd need to gather the info country by country. There may also be small, unregistered airplanes that have engines. You can download the US list as a starting point https://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/releasable_aircraft_download/

Difficult one this.  Registered aircraft that don't have engines include balloons and sailplanes, but there are also aircraft that don't need to be registered such as hang gliders and paragliders.  Then there are wingsuits, which are sort of gliders with an atrocious glide ratio, and if you include those, what about parachutes?

All airplanes have engines, the definition of an airplane (or aeroplane) is:

A powered flying vehicle with fixed wings and a weight greater than
  that of the air it displaces.

There are aircraft that do not have engines, for instance gliders.

Also free balloons.


text:
NOTAM - What means "no shoulders along taxiways" in German?
can anyone explain to me what "no shoulders along taxiways" means?
I know what shoulder markings are, but I don't know how to translate them.
Are there German people? :)
Thank you!

Welcome to Aviation.SE! The taxiway shoulder markings are placed beyond the taxiway borders to mark unusuable parts of the taxiway. In German you could call it „Rollweg-Randstreifen“. Do you have reference which airport this NOTAM Came from?

Thanks! Oh "Rollweg-Randstreifen" sounds good! Here is the full NOTAM: Taxiway A closed for all operations, work in progress on shoulders along edges of RWY; WEF 1 APR until 26...

@pcfreakxx I googled it. The actual text might be from http://students.radiocheck.at/uebersetzungstexte.pdf The document is an exercise book for translating phrases used in radio communications. And the very same document includes this German translation: "Rollweg A für jeden Betrieb gesperrt, Arbeiten auf den Schultern entlang der Pistenränder im Gange; mit Wirkung vom 1. April bis 26. April." Indeed, "shoulder" is "Schulter" in German and the "Straßenschulter" (street shoulder) is the area beneath a paved road.

The NOTAM you copy doesn't mention taxiway shoulders anywhere. It says there is work going on on the shoulders of the runway and apron, and that a taxiway is closed.
As to taxiways not having shoulders, quite possible. The hard shoulder is the area outside the marked road surface, this can sometimes be extremely narrow.


text:
How do I calculate top of climb?
How can I calculate the distance on the ground during the climb?
Assuming the climb power is 700ft/min, the climb speed is 65 kts, the wind 260/10kts on runway 26.
Start: 700ft
Top of climb: 3500ft
How far is the distance flown on the ground (in e.g. ft) and the GS?
What I understood:
The difference in altitude is 2800ft and therefore 2800ft / 700ft min = 4 minutes. I can say that I fly 4 minutes long 65 knots:
65kts -> 6582 ft * 4 = 26 328 ft but I don't use the wind in this calculation.
Can someone please help me?
Thanks!

How much did the air mass (wind) travel in four minutes?

That 65kts "climb speed" -- is that ground speed or air speed?
If it's ground speed, then you already have your answer. Since the question is about ground speed and distance travelled, then the wind doesn't factor in to it.
If it's air speed (which is far, far more likely), then you need to figure out your ground speed first. This is where the wind comes in. Now, you didn't specify which direction you're flying, but we can assume from the mention of "runway 26" that you're flying 260 degrees. That means you're flying into a direct headwind, which means in turn that your ground speed is simply your airspeed minus the wind speed. Then use that value in your distance calculation.

Thanks for your help! Correct, 65 knots is airspeed. But I don‘t understand why the GS is just airspeed minus wind? If I climb with an angle of (almost) 89 degrees (or 100.000ft/min) than the GS can never be 65-10kts because it is something else as to climb with an angle of 1 degree (or about 10ft/min) isn‘t it?

65kts with a 700ft/min climb gives a climb angle of 6.7 degrees, so that the horizontal component of the speed is 65*cos(6.7)=64.6 so you typically neglect those 0.4 knots. Other errors as exact wind speed will be bigger.

Thanks, good argument :) That's it!


text:
Are MSN numbers unique
Is it possible for two aircraft to have the same MSN number,  I was under the assumption the an MSN was a unique identifier for an aircraft

Each manufacturer has its own conventions. For example, Airbus only use MSN (which is only unique per aircraft type). Boeing on the other hand uses both an MSN and "line number". Boeing's "line number" is unique per aircraft type (like Airbus's MSN) but the MSN is unique across all aircraft types.
Other manufacturers may or may not have the same conventions.


text:
Does the glide slope flag detect percent of modulation (80%)?
Please advise if the glideslope flag validates that the received frequency is being modulated at nominal 80% or 40% for a localizer.

I wanted to post this as a comment, but it's a bit long.
From ICAO Chicago Convention annex 10, vol 1:

2.3 Alarm conditions for ILS airborne equipment
2.3.1 Ideally, a receiver alarm system such as a visual flag should warn a pilot
of any unacceptable malfunctioning conditions which might
arise within either the ground or airborne equipments. The extent to
which such an ideal may be satisfied is specified below.
...
2.3.3 The alarm system should indicate to the pilot and to any other airborne system which may be utilizing the localizer and glide path
data, the existence of any of the following conditions:
...
b) the percentage modulation of either the 90 Hz or 150 Hz signal
reduction to zero with the other maintained at its normal 20 per cent
and 40 per cent modulation respectively for the localizer and glide
path;
Note.— It is expected that the localizer alarm occur when either the
90 Hz or 150 Hz modulation is reduced to 10 per cent with the other
maintained at its normal 20 per cent. It is expected that the glide
path alarm occur when either the 90 Hz or 150 Hz modulation is reduced
to 20 per cent with the other maintained at its normal 40 per cent.

Glide path receiving equipment operational standards are detailed in RTCA DO-192 and EUROCAE ED-47B


text:
Has mod percent changed for Mark-1 glide slopes?
Mark-1F glide slopes operate at 80 percent modulation. What was it for earlier versions i. e. Mark-1C, Mark-1D, etc.

By "Mark-1" you are likely referring to Wilcox Electrics Mark-1A, C, D and E and Eaton/AIL Mark-1B deployed by FAA in the US. ILS GS are expected to be compliant with ICAO Annex 10. To check whether the ICAO specifications changed, could you tell us the years these models were sold/deployed? 1B seems to be around 1980.

I think I figured out the answer, but won’t select it for a few days to allow input from others.

The percentage of modulation hasn’t changed, rather the way it is measured. Upon further review the current measurement is 80% SDM (sum), where before the measured value was 40% for 90 & 150 hertz individually. The method of measurement change, may be due to rare case instances where 90 and 150 shouldn’t be exactly equal, but together the sum is always 80%.


text:
Which airspace requires what RNP?
How do I know which airspace requires what RNP value? More specifically, can I go from NY to London with just BRNAV providing I stay above the NAT HLA?

Check the local AIP.

For completeness, Please refer to the following website:
https://www.uasc.com/docs/default-source/documents/whitepapers/uasc_rnp-rnav_whitepaper.pdf
Here are some extracts that allow to compare US and European requirements:

US Airspace Requirements
The current US RNP requirements are:

RNP-10 as described in FAA order 8400.12c
RNP-4 as described in FAA Order 8400.33
RNAV (RNP AR) approach authorization as defined in Advisory Circular (AC) 90-101a
Basic RNP capability is achieved through TSO-C146 compliant equipment when installed under AC 20-138().

RNP-10 and RNP-4 procedures are limited primarily to oceanic airspace.
RNAV (RNP AR) procedures are available in the US for domestic
  operations. These procedures require approval, hence the name:
  Authorization Required (AR), formally known as Special Aircraft &
  Aircrew Authorization Requirements (SAAAR) procedures.
European Airspace Requirements
There are two existing European RNP requirements:

Basic-RNAV (B-RNAV), equivalent to RNP-5 (reference FAA AC 90-45A, AC 20-130, AC 20-138, and AC 25-15)
Precision-RNAV (P-RNAV), equivalent to RNP-1.

These requirements are defined in European Aviation Safety Agency
  (EASA) Temporary Guidance Leaflet (TGL)-10, and FAA AC 90-96A. A
  statement is required in the Aircraft Flight Manual (AFM) or AFM
  Supplement (AFMS).
For European operations, a Letter of Authorization (LOA) for all RNP
  operations, is necessary, as the requirements differ from the FAA
  requirements.


text:
How do dry bays protect against fire?
How do dry bays protect against fire, and do civil aircraft also have dry bays like military aircraft?

The article you linked to doesn't state that dry bays protect against fire. Quite the opposite: it states that dry bays are fire hazards, which is precisely why they need to be kept dry.

Yes, civil also aircraft have “Dry Bays” but they do not protect against fire. A dry bay is an area adjacent to a fuel tank that holds various components.
Some aircraft (mostly military?) have fire extinguishers or fire suppression equipment in dry bays but this will vary considerably with each type. (the B777 has no fire suppression in the dry bays)

Thanks, I edited my answer to include info from your link.


text:
The state of the art of scramjet engine
What is the state of the art of the scramjet engine? Which nation is at the envelope of that technology? This is a follow-up to this question.


text:
Is the engine of 3M22 Zircon truly scramjet?
I have the impression that no scramjet has been realized so far. But the engine of 3M22 Zircon is reported to be a scramjet. Is it really a scramjet?

Perhaps the hypothetical design you're thinking of is a shcramjet, not a scramjet? https://en.m.wikipedia.org/wiki/Shcramjet

@Someone: Why do you think so? The US program only just started testing: https://en.wikipedia.org/wiki/Hypersonic_Air-breathing_Weapon_Concept

The schramjet is still hypothetical, and the name is quite similar, so I was wondering if you heard/read that shcramjets are still hypothetical, and thought it was referring to scramjets.

@Someone: I see. This is the first time I heard of schramjet. Good to know.

Speculatively possible.
I've searched if the manufacturer has made such a claim. However, they aren't making any claims. The only explicit claims they make is a press reprint about the specifications: that it flies at 2.65 km/s at an altitude of 20 km. Your link includes verified range figures of 350, 450, then 1000 km.
Perhaps one could determine if it's likely to be a scramjet indirectly, by analyzing if this performance could have been reached by another type of engine. First checking rockets:

The first 2.65 km/s of delta-V goes towards acceleration. For a (very good) solid rocket motor at Isp~=265, that requires Wi/Wf=e, in other words, 63% of the missile's mass just to get it to speed. 70% or more if the motor is discarded.
The Breguet equation for range in sustained aerodynamic flight is R = V * L/D * Isp * ln (Wi/Wf).
At a roughly estimated L/D=3 and fuel weight fraction of 0.35, R = 2650 * 3 * Isp * 0.43 ~= 3400 * Isp, for range in meters.
Solid rocket propellant would produce Isp in the 230-270 range, giving a range of 850 km. This is close enough to 1000 km if some speed is traded for range or L/D exceeds 3.

It's not easy to research a weapon that's still under a lot of secrecy. I had hoped that Russian-language articles would be closer to the source, as they usually are, but all are clearly the work of analysts not involved in the missile's development. This is the best I've managed to find. It confirms again that the missile uses a synthetic hydrocarbon fuel (JP-10 equivalent) and "a special ramjet engine, which is characterized by supersonic combustion". That would be the definition of a scramjet.
Another article digs into listing every test, including launch footage, and attempting to estimate the missile's exact shape and dimensions from OSINT.
Mass is not advertised, but considering that the Zircon is a bit smaller than the missile it replaces, it can't be more than 3,000 kg total. That leaves a maximum weight of 900 kg for the second stage. With 35% for fuel and 30% for airframe+engine, its weight budget falls 20-25% short of that required to fit a 300 kg warhead and at least 100 kg in avionics.
So, it's possible to achieve the 350-450 km range from early tests without using a scramjet engine. A combination of rockets or air-augmented rockets could reach this velocity and range. For the later long-range tests, the warhead would have to be removed or greatly reduced.
Overall, a rocket engine is very unlikely. This missile is a successor of a long line of ramjet missiles. Its shape clearly indicates an airbreathing engine inside. The manufacturer doesn't explicitly state they're using a scramjet, but regular ramjets or other engines can't run at Mach 7. Scramjet engines have been studied and tested extensively, in various forms, and could realistically be used there.
Changing the equations to use a rocket to get to half speed, then a scramjet for the rest brings different math:

Accelerating to 1.3 km/s with a solid rocket requires 40% mass in fuel, or 45% with the motor.
Assuming a very conservative 700s Isp for the main engine, the remaining 1.4 km/s will take 1-1/e^(1400/7000)=18% mass in fuel.
The Breguet equation, after removing 18% spent on acceleration, computes as R = 2650 * 3 * 700 * ln(0.82/0.65) ~= 1,292,927, i.e. ~1,290 km.
To reach the target range of 1,500 km, fuel fraction has to be increased a bit. At 40% fuel, estimated range increases to 1,738 km, so it would be in between.
For a second stage at 1650 kg total, possible weight breakdown computes as 660 kg (40%) fuel, 550 kg airframe+engine, 340 kg warhead, 100 kg guidance.

The missile looks like it has a smaller booster than 45% by weight, though. But it's possible, considering that the second stage has a non-circular shape.
More likely, the missile uses a dual-mode ramjet, rather than a straight scramjet. Unlike the rest I've had to refer to, this article comes from a trusted source, having been published by the Von Karman Institute and republished by NATO.
Dual mode ramjets are a cross between ramjets and scramjets, able to operate in both subsonic and supersonic combustion modes. A DMR allows for an earlier takeover from booster to primary engine, improving range and payload capacity.
Of particular interest is the joint program between MBDA (French missile manufacturer) and MAI (Russian aviation research center) to develop a "wide range ramjet" and a "dual mode ramjet", covering the range from Mach 2 to Mach 12. The program was extensive on both sides, with a lot of prototypes. According to the article, testing at MAI's hypersonic wind tunnel has validated Mach 2-7.5 wide-range ramjet engines. It appears that this program has culminated in the Meteor missile using a wide-range ramjet and the Zircon missile using a dual-mode ramjet engine.
A DMR is also more consistent with modest statements about a "special ramjet supporting supersonic combustion", rather than an entirely different engine.
With a dual-mode ramjet, range estimates change:

Solid rocket booster is needed up to 700 m/s, consuming 26% mass in fuel, or 30% including the motor.
At the same 700s Isp for the DMR, the remaining 2 km/s will take 1-1/e^(2000/7000)=25% mass in fuel.
Using another 15% for cruise, Breguet computes as R = 2650 * 3 * 700 * ln(0.75/0.60) ~= 1,241 km.
At 2000 kg, the second stage might include 800 kg fuel, 600 kg airframe+engine, 400 kg warhead, and 200 kg guidance.

That version is consistent with current and intended range, is on the lower end for booster size, and leaves margins for heavier guidance or lighter launch weight. 2,850 kg is assumed here, but it could be as little as 2,000-2,400 kg with a lighter airframe or guidance package. It's also possible that the ramjet takes over a little later, maybe at Mach 3, driving a larger booster and a smaller second stage.
Summary

The missile's specifications are consistent with a scramjet engine.
A dual-mode ramjet is also a possibility, consistent with the missile's specifications, history, appearance, and research programs.
Test results are not consistent with other engine types. Rockets could replicate them, but with no room for a warhead.
The engine appears to be a "live prototype" that's still being improved. It falls short of the theoretical abilities of a scramjet, being more similar to an early iteration.

Care to look at my follow-up question https://aviation.stackexchange.com/q/100838/37156?

@Hans Seen it. It's a very difficult question to answer. Much of that knowledge is TS/SCI or local equivalent. While there's some hope that scramjets will result in hypersonic passenger aircraft, right now their most likely application is missiles that destroy billion-dollar warships without warning. I'll try to respond with what I can produce based on open data.

Most likely. However very little info on the Zircon except anecdote and some leaked material.

Building a scramjet isn't necessarily hard, managing the missile in flight is the challenge.


text:
Departure and arrival fix loading via FAA website
About 8 years ago I was involved in a project that would hit an FAA website for fix loading. It was departure and arrival fixes and their associated data. The URL included a command line where you could request an airport, date, time, and increment. Does anyone know what happned to that site or if there is a replacement? The data looked something like this:

Do you know the original URL you were using at the time?

It's an IP address.

All URLs correspond to an IP address. Would still be helpful if you could post it.

The FAA has a graphical display of forecast arrivals by arrival fix for airports in the Airport Arrival Demand Chart. Choose a time interval, airport, and select "arrival fix." If you look at what it's doing through a network inspector, you'll see it's fetching JSON data, if you're looking for programmatic access.
That page only shows arrivals, not departures though.

Very interesting. Let me follow up on that


text:
Do commercial flights continue with an engine out?
Do commercial flights continue with an engine failure? If you look closely at the attached picture it seems that one of the engines has a much smaller contrail than the other three. This seems to suggest that the aircraft is flying on three engines with the one at reduced (idle?) power. Is this normal?

The chemtrail tank for one of the engines ran dry. Perfectly normal. Try not to think about it.

The image looks like four engines running at the same cruise thrust. The wake vortex is blowing the exhaust of the inboard engines down and the exhaust of the outboard engines out and in the perspective of this image this makes the lower two streams look merged while the upper ones further apart. Close behind the engines it is clear there is four of them and all have similar strength.
That said, a four-engine aircraft may continue on three engines as far as it has enough fuel and there is no other damage (so not if the engine flamed out after a big bang). With one engine out it can't maintain as high altitude, so it has to drift down to lower altitude where it flies slower and thus has shorter range. However if they have enough contingency fuel, they can continue to destination. Or return back to departure point, or proceed towards the destination, but land somewhere short. The dispatcher will consider the repairs, taking care of the passengers, rebooking them, the next flight the plane was scheduled for and other things and tell the pilots which is the preferred option.
In contrast a two-engine aircraft shall land as soon as possible. One engine out of two means there is no redundancy left and that is an emergency and shall be handled as such. Note that as soon as possible does not necessarily mean closest airport—the aircraft will cover over 100 NM during normal descent from cruise altitude, so if there are more options in about 150 NM, the pilots and dispatcher still get to choose.

"Land as soon as possible" may give the wrong impression, since twin engine aircraft are routinely used for flights over oceans. In fact the longest flight certification for a twin engine aircraft after an engine failure is now 370 minutes (just over 6 hours) before landing for the Airbus  A350XWB.

@alephzero If the nearest airport is indeed 370 single-engine minutes away, then there's no choice. But FAA rules (Part 121.565) are specific in that you must land with the least amount of flight time unless there's a safety reason, and in that case you must file a report with the FAA. The common term is "land at nearest suitable airport".

@JanHudec Those are the two usual terms used in emergencies and have a distinction. "Land as soon as possible" means to get the plane down as fast as possible and consider places such as too short runways, closed airfields or the Hudson river (Airbus would call it a red LAND ASAP). "Land at nearest suitable airport" means no immediate danger and consider runway length, crash services, familiarity, terrain, etc (Yellow LAND ASAP in Airbus philosophy). The term "nearest suitable airport" is written into regulation (121.565)

But isn't it still an extra risk for a two-engine aircraft to target a distant airport? Say you're right above a suitable airport (no extra danger landing there, maybe inconvenient for the passengers/operator), but you target another airport 100 NM away, well outside of your glide range. If your second engine fails midway, won't that leave you unable to land at either airport?

@wrtlprnft 100 NM isn't well outside of your glide range in an airliner at cruise altitude. That's actually pretty close to your glide range. Airliners can glide a really long way from cruise altitude. Also, midway between two airports 100 NM apart, you are 50 NM from each of them, well within the glide range of most airliners.

I know someone who flies the A380. Last summer they had an oil leak on #3. I don't know the full details, but do know they left it running at idle and continued to their destination.

@wrtlprnft If you're "right above" an airport, and at or near cruise altitude, you can't land at that airport, at least not immediately. It takes time - distance - to descend. If you have no other good options where to land then you certainly can do something like a circling descent (think corkscrew, or descending while flying something similar to a holding pattern), but you wouldn't be getting down much sooner because of it. So if you're at cruising altitude straight above an airport and need to land, that airport 100 NM away with a longer runway or better weather may well be a better option.

I'd have thought that landing soon is not the top priority if the aircraft has no other problems than the engine failure. I'd just have assumed that you want to try very hard to leave the glide slope of a suitable runway. If that takes an hour of descending in a pattern, so be it. My back-of-the-envelope calculation would be that reaching 200 km distance out of 10 km altitude would require a glide ratio of 1:20, which seems to be at least at the upper end for airliners.

authors: Bob Jarvis - Слава Україні


text:
What is this yellow tube blowing air?
What is this yellow tube (lower right quadrant of the picture) which is blowing air into the airplane while it's at the terminal? You can see the open hatch on the bottom of the jet through which it's connected.

Most likely it’s a compressed air line which connects into the jet’s bleed air system.  This can be used to crank the engines as opposed to using bleed APU air to do it.
Another use (if you’re talking about the line under the jetway) is to provide cool air for cabin air conditioning without needing to run the APU to do so.

The tube looks quite thin and flimsy, like it's made of a light fabric. Do you think there is a compressed air line inside it?

I think you're confused, the yellow pipe with black ribs under the jetway on the right side of the picture, is pre-cooled air feed into the mix manifold so the plane doesn't need to run the air conditioners, which in turn need the APU to be on (which causes local polution). There another pipe which is orange on the left side of the picture which joins the aircraft just under the door, which looks like a compressed air line.

Conditioned air.  Start air has a smaller diameter.

Well there’s two different items here.  There the large tube under the jetway then a smaller one running under the aircraft and connected to it by an access port on the belly.  I can’t twll which one the OP is indicating.


text:
Why was Air India flight AI101 diverted to SHJ 5 times in the past few days?

Air India flight AI101 using a 777-300ER on multiple westbound and eastbound routes was diverted to SHJ airport in Sharjah, UAE. I am curious if there is a specific reason. It cannot be a coincidence 5 times to the same airport.
Link to flight history: https://www.flightradar24.com/data/flights/ai101

Could be the airline has reassigned the flight number to the SHJ route or introduced a stopover, while Flightradar24 still thinks it should go direct to New York when in fact it is planned to SHJ. Have you checked another website (preferably the airline‘s one) for where the flight is scheduled to?

@CptReynolds I can't find any indication of the flight having a stopover. All sites list it as a DEL-JFK non-stop

Is it possible that they don't have the range to get to JFK without stopping for fuel due to the Pakistan Airspace Closures/Restrictions. Looking at the dates, it seems that the flights started diverting when the India/Pakistan tensions flared up a week ago (~Feb 28).
https://www.flightradar24.com/blog/tensions-between-india-and-pakistan-affect-air-traffic/
Going to Sharjah for the diversion avoids the Pakistani airspace as seen below:

https://www.flightradar24.com/data/flights/ai101#1fb4a663

You may have hit the jackpot. According to Great Circle Mapper DEL-JFK is 7,318 mi direct. The 777-300ER has a MTOW range of 7,370 nmi. Factoring in the closure of Pakistani airspace + the fact the flight more than likely does not fly the great circle route, it is a very good probability that the the aircraft simply does not have enough fuel.

Wow that seems to cut it close regardless of the airspace closure!

Indeed pretty close, but I bet these flights do not take-off with full payload (ie, passengers) so they can probably squeeze few more miles.

@zymhan Whether or not it "seems to cut it close" depends on whether the quoted max range includes burning required reserve fuel or not. My guess is that it's max no-wind range and landing with the required reserve. If that's the case, it would be normal to flight plan right up to that limit. Of course, the limit wouldn't really be in distance but rather time in the air since wind will always be a factor.


text:
How much can 3 fans 7 inches in diameter and each a generating 160 cubic feet per minute airflow rate lift?
I'm working on a hoverboard project and am having trouble finding out the maximum weight these fans could lift.

How is a question about building a hoverboard on-topic here?

Weren't there a bunch of hoverboard questions around 18mo ago??

You have volumetric flow rate and diameter, so you have the $\Delta v$ ($v = A \dot V$) and you have the mass flow rate ($\dot m = \varrho \dot V$) and that gives you the momentum per unit of time a.k.a. force ($\dot p = \Delta v\cdot\dot m = F$).
Run the numbers yourself, but don't get high hopes—the result is tiny (of course; you need a couple of metres diameter to lift a human with useful efficiency).

Of course, the amount of force is much higher if the hovercraft is operated in ground effect, in which case the amount of force is simply $F=\Delta p \times A$ with $\Delta p$ the pressure difference across the fans (probably a function of leakage flow at the edge of the hovercraft) and $A$ the surface area of the hovercraft.

@Sanchises, but can you actually derive $\Delta p$ from the known parameters? Also I wouldn't really agree with the qualification “much”. It will probably be several times, but given how tiny the force actually is, it does not make it much more practical.

No, I don't suppose you can, that's entirely dependent on the fan characteristics. It makes a large difference for a hovercraft if these fans could deliver this volumetric flow at hundreds of kPa or a few Pa. I guess my main point is that for a hovercraft, you don't want thrust but $\Delta p$. Then again I'm not what a hoverboard is.

Taking the conclusion of Hudec's answer:
$ \Delta v\cdot\dot m = F$
First of all, let's use decent SI units...
3 x 160 cu ft/min = 0.22653 cubic meters/sec. As they pass through those fan apertures (total 0.07444 sq. meters) in one second, the airspeed of that mass is 0.22653/0.07444 = 3.0431 m/s. If the change of speed is from zero, then $ \Delta v\ =$ 3.0431 m/s
Now, 160 cu ft of air = 0.07551 cu. meters = 0.0928 kg (density of air = 1,23 kg/m3)
Inserting numbers in Hudec's expression:  3.0431 m/s x 0.0928 kg/s = 0.2822 N
A very tiny force indeed...

You used the flow from one fan and the area of all three, so your velocity is wrong.

@aml You're right. Correction introduced...

(Jan Hudec's answer is correct but probably hard to understand.)
You want Force and you know flow (cfm =$ft^3/minute$) and area ($\pi r^2$).  Force is mass times its acceleration.  Mass is weight/gravitational acceleration, and the acceleration of that mass is its change in velocity over time, so $F=(W/g)*(\Delta v/t)$.  The starting velocity of the air is zero, and each fan gives it a velocity of flow/area.  The weight of air moved in a given time is flow*density (sea level air weighs about 0.076 lb/cu.ft.).
Make sure that you use the same units throughout (for length, time and weight) and multiply by the 3 fans when done.
This force is the total thrust and therefore the maximum weight that you could fly freely (you will find that it is very small).
If you are making a 'hovercraft' with a skirt then you are just reducing friction rather than flying (the pressure of the trapped air comes into play).

please consider using MathJax markup for mathematical symbols and equations. also, a linebreak here and there helps with readability.

@Federico - thank you -- is there a tutorial I should see?

if you ever used LaTeX, the syntax is basically the same. Otherwise, you can have a look at the official website: https://www.mathjax.org/#docs


text:
When extreme yoke movement cuts out stab trim on a 737-NG, does it stay off after yoke returns from limits?
I've read that the 737-NG has logic built into the stab trim system that will cause stab trim to cut out if the control column (yoke) is pulled/pushed far/hard enough (it's not clear to me if it's travel distance or force thsf causes the cut out).
My question is, given the control column stab trim cutout mentioned above, does it continue to function after the control column is moved back from its hard stops or force is decreased  below a certain value?

From the Boeing 737 NG FCOM v2 (9.20.8 Flight Controls - System Description):

Control column actuated stabilizer trim cutout switches stop operation of the main
  electric and autopilot trim when the control column movement opposes trim
  direction. When the STAB TRIM override switch is positioned to OVERRIDE,
  electric trim can be used regardless of control column position.

So any opposite movement of the yoke will stop the stab trim. There is nothing mentioned in the FCOM about staying off, so I would assume stab trim would continue immediately after the yoke is released.

no, it doesn’t stay off.
further, as we know by now, the yoke has no effect on the MCAS AUTOTRIM on the B 737 max; it is terrific.


text:
Who applies an airworthiness directive when the airframe is newer than the AD?
For example, an AD was issued in 1990 while the aircraft was manufactured in 2002? Who applies the AD, the manufacturer or the owner?

I am interpreting your question as asking whether an owner of an aircraft is responsible for complying with ADs that were issued before the aircraft was manufactured.
Short answer: yes.
There are several types of ADs that affect your aircraft. Some of them apply to all aircraft of a specific type, some apply to specific serial numbers or model numbers, and some apply to specific parts that are installed on your aircraft.
Some are one-time and others are recurring. The one-time items would usually have been checked before the airplane left the factory. The exception would be if they were required after a certain number of airframe hours. Recurring items can still apply to all aircraft—even those made after the AD was issued.
The two ADs listed below require the owner to check for excessive wear in the listed parts. I just replaced the Bendix switch in my Cherokee because it failed the required test in the AD.
Here’s one that was issued in 2011 for all Cessna aircraft AD 2011-10-09:

We are superseding an existing airworthiness directive (AD) for Cessna
  Aircraft Company (Cessna) 150, 152, 170, 172, 175, 177, 180, 182, 185,
  188, 190, 195, 206, 207, 210, T303, 336, and 337 series airplanes.
  That AD currently requires repetitive inspections and replacement of
  parts, if necessary, of the seat rail and seat rail holes;

Here’s one that was issued in 1976 that applies to all aircraft that have Bendix ignition switches AD 76-07-12:

Applies to all aircraft employing magnetos and using Bendix ignition
  switches listed in the table below except switches identified by four
  digit date code (new) adjacent to the model number or a white dot
  (modified) on the support plate adjacent to the Bendix logo.

Your A&P should have software that allows them to easily check which ADs apply to your aircraft and then create an AD Compliance Report for you. It will list all of the ADs and the date that they were complied with. Most reports also list ADs that apply to your aircraft model, but are excluded by serial number.


text:
How is flyblackbird.com operating under Part 91K?
The website states they're not a Part 380. Love their service -- how will they avoid the same fate as Flytenow?

Long story short, Blackbird appears to be set up so that the customer leases an aircraft and separately hires a pilot to fly it. That makes it a 'straight' part 91 operation. However, the FAA has stated that pilots using Blackbird are holding out and require part 119/135 certificates (with some technical exceptions, such as 91K).

Blackbird's terms and conditions for pilots specifically mention 91 B but not K and include a few interesting points (emphasis mine):

Pilot services are offered as an independent contractor to users under a dry lease
The pilot is not directly employed by the owner of the airplane
The pilot operating the flight cannot own the aircraft being rented
Pilot hiring is at the discretion of the passenger; BlackBird will facilitate matching pilots with aircraft based on passenger
  selected routes, pilot qualifications, and location and availability
  of both pilot and aircraft
Pilot understands that passenger (lessee) renting the aircraft and hiring the pilot accept and maintain operational control of the flight; these operational duties may be delegated to the pilot in command.

In other words, the passenger rents an aircraft from an owner and then separately hires a pilot to fly it, according to the passenger's instructions. Blackbird is saying that they only provide a marketplace, and the customers actually lease and operate the aircraft themselves.
This is from their general term and conditions:

The Platform provides a marketplace that enables users to (a) connect
  with and lease aircraft from third parties that own, lease, or
  otherwise control aircraft (“Aircraft Owners”) and to find and hire
  flight crews (“Flight Crews”), or (b) join flights with third-party
  operators or other BlackBird users on the Platform (“Third-Party
  Operators”).

And:

If you wish to lease an aircraft from an Aircraft Owner and / or hire
  qualified Flight Crew, then you can use the Platform to search for
  available aircraft and Flight Crew

Because the owner just rents out the aircraft without a pilot, they aren't operating an air carrier. Because the pilot doesn't provide the aircraft, they aren't holding out. That means the only pilot qualification needed is a commercial certificate, although Blackbird also requires 500hrs, an instrument rating and a background check.
Now, whether or not that business model will survive if the FAA gets interested in it is another question. There was some discussion on the AOPA forums (members only) a while ago about Blackbird and I think the consensus came down to "technically legal, but pushing their luck with the FAA and DOT".
A semi-useful comparison here might be Uber. They've always claimed that they aren't a transportation company but rather a marketplace that just connects independent drivers with customers. That argument has succeeded in some places but not in others, and many countries and cities have decided that Uber is a transportation company and started regulating them. I have no idea whether or not that will happen with Blackbird.

Update: on December 17th, 2019 the FAA made its opinion very clear in a letter to Blackbird's lawyers:

The information that BlackBird has presented leads us to conclude that
  the pilots participating in BlackBird's platform and using its app are
  holding out and thus are engaged in common carriage.

If you're a pilot who flew via Blackbird, their closing statement isn't reassuring:

Accordingly, please expect further investigative activity into
  BlackBird's operations, particularly regarding its pilot database. In
  addition, we would be interested in learning of any action you intend
  to take in view of the jeopardy facing pilots who participate in
  BlackBird' s service.

There's a lot more discussion online, especially in Reddit (/r/flying) if you want to read more.

General aviation aircraft leasing has come under some scrutiny in Europe recently, following the death of footballer Emiliano Sala, and USA-registered aircraft were involved in the series of flights before the fatal crash. The FAA may be "encouraged" to get interested in this legal area …. https://www.bbc.co.uk/news/uk-wales-47626855

Due to the FAA letter in late December 2019, this answer is no longer applicable.

@wbeard52 Maybe. Blackbird could challenge the FAA in court, as Flytenow did. I know I have an interest in this answer, but if it isn't applicable then what is? For now, at least :-)

I don't think the FAA will allow untrained or unqualified pilots from ever providing air taxi service.  Services like these push the boundaries but the FAA will insist they follow Part 119 regulations.  The answer by Jason Blair is more correct now.  I am pretty sure Blackbird's fate will be the same as FlyteNow.

In an FAA letter this week…

We have considered the June 10, 2019 letter from BlackBird Air, Inc. (BlackBird), that set out many aspects of its business model and operating assumptions. The information that BlackBird has presented leads us to conclude that the pilots participating in BlackBird's platform and using its app are holding out and thus are engaged in common carriage.

Going on...

In sum, the FAA has concluded that pilots' use of the Black:Bird platform constitutes "holding out" and participating pilots are engaged in common carriage. Because these operations are subject to part 119 certification, a pilot who holds an airline transport pilot or commercial pilot certificate must obtain and hold a certificate issued under part 135 or the pilot must be employed by a company operating the flight that is certificated under part 119.

And...

Accordingly, please expect further investigative activity into BlackBird's operations, particularly regarding its pilot database.

You can read the full letter here


text:
Why does MH370 Satellite data disagree with track after take off?
Can someone please explain the inconsistency in MH370's alleged track after take off?

The satellite handshake offset frequency shows an increase after take off until 16:55 UTC, then a reduction in frequency until 17:07 UTC.
A frequency increase means signal compression, in other words flying west towards INMARSAT.
The problem is after take off at 16:41 UTC MH370 was tracked by radar flying steadily east until reaching BITOD (east of IGARI) when tracking ceased at about the radar horizon. MH370 was never spotted on radar east of the Malay peninsula flying back.
In the preliminary accident report released on May 1st by the Malaysian Government it is shown flying back to Penang. Radar tracking imagery from Butterworth shown to relatives at Beijing on 21 March shows a target flying from Penang at 18:02 UTC across VAMPI and reaching MEKAR at 18:22 UTC.
My question is why the satellite handshake data does not match the claimed track?
The frequency increase implies MH370 flew west after 17:07 UTC, but the radar/transponder  data says it continued east until at least 17:24 UTC.
The other problem is that after 18:25 UTC the satellite data implies MH370 flew away from the satellite.
The satellite movement from take-off until 19:41 UTC was northward from the horizon and INMARSAT's displacement does not seem sufficient to cause the inconsistency.

It is not a duplicate since it relates to a different portion of the track at a different time period. The answers in relation to this period of the flight may be entirely irrelevant to a later part of the flight or may not address the question posed for another part of the flight.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Why do MH370 Indian Ocean INMARSAT distances increase when they should decrease?
This image illustrates my question:

In the Burst Offset Frequency chart from 19:41 UTC until the final ping at 00:11 UTC the blue track for MH370 shows increasing frequency, which means flying towards the satellite.
Therefore for the Burst Offset Frequency chart to be correct the flight track in maps released by the preliminary accident report should have curved west not east.
If they were fundamentally so wrong how could this ping chart ever have been used to plot the final location of MH370?

The "frequency offset" is a Doppler-effect-derived value.  It's related to the speed of the aircraft towards/away from the satellite, not its distance; the rising line is consistent with an aircraft slowly turning away from the satellite.  (It's also consistent with the aircraft performing a number of more improbable maneuvers, which is why the chart is simply the most likely track.)

If the BOF chart shows constantly increasing velocity towards the satellite, then the track distance should also reflect that. The problem is not my interpretation. The aircraft could not have flown the track suggested and give the offset frequency values reported. One or other is a lie and the lie is the official accident report's track which is a mere speculation.

"You assume that an increasing velocity towards the satellite means decreasing distance towards the satellite. That is false." Why? If I run towards you with increasing velocity, my distance from you will decrease, obviously.

It seems to me that your question is based on a misinterpretation of the data, as already noted in this aswer to another (extremely similar) question you asked.
You say

In the Burst Offset Frequency chart from 19:41 UTC until the final ping at 00:11 UTC the blue track for MH370 shows increasing frequency

That is a statement that contradicts itself.
The chart shows the offset, not the frequency, an increasing offset can mean both decreasing or increasing frequency, depending on the sign.
Most likely only the absolute value of the offset has been plotted for convinience.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Are the nearby airplanes cleared of the sky when launching Falcon Heavy?
I was checking Flightradar24 when launch occurred and didn't see any difference. Also, 3 boosters landed back successfully. I assume the sky has to be clear of airplanes to avoid any potential collision?

SpaceX launches from Cape Canaveral Air Force Station (CCAFS), Vandenberg Air Force Base (VAFB), and Kennedy Space Center (KSC). All three have Restricted/Warning areas overhead and out to sea, from the surface to "unlimited" (i.e. space). It is illegal to fly through active Restricted airspace without permission. Warning areas are used over international waters and thus flying through them is not illegal, but they give fair warning you may not survive the experience, so pilots treat them the same.
These areas aren't active full time, but since activation of these areas is unpredictable (most have fixed schedules), airlines never plan flights to pass through them; it's simpler to fly around them every time, even though most of the time it isn't necessary.
GA flights, though, are quite common in those areas when they're inactive; ATC will allow flying over the launch areas, landing facilities, etc. as low as 500ft. When they're active, it's not uncommon for dozens of GA planes to be circling just outside the area to get the best view of the rockets, both going up and coming back down. However, GA flights don't show up on most flight tracking web sites by default, so you may not be seeing them.